Project Summary Several clinical trials have found that intranasal oxytocin (OT) treatment is not practically viable in its current form for improving core social symptoms in autism spectrum disorders (ASD). The current intranasal OT treatment has been criticized for its often weak and inconsistent effects, demanding an important need to explore new ways to improve its efficacy and reliability in modulating the OT system. While much less studied, the central opioid system has also been implicated in ASD based on the opioid dysregulation found in certain cases of ASD, as well as the well-known modulatory effects of opioid agonists, such as morphine, and its receptor antagonists, such as naloxone (NAL), in regulating social behaviors. In this translational non-human primate proposal, we will investigate a new alternative therapeutic option in improving core social functions by exploiting the robust regulatory relationship between the central OT and opioid systems. Our pharmacological study in non-human primates recently provided a proof of concept of this combined pharmacological approach in more effectively modulating social attention. The combined intranasal administration of OT and NAL (OTNAL) enhanced spontaneous social attention and contingent gaze dynamics following interactive eye contact over and beyond the summed effects from administering OT alone and NAL alone, indicating a combinatorial benefit of OTNAL. Capitalizing on this finding, we now propose to determine the optimal doses of OT and NAL in the combined OTNAL format, its corresponding cerebrospinal fluid markers of successful OTNAL interventions, as well as the neurophysiological markers underlying the combinatorial benefits in the domain of social attention. We will first obtain comprehensive dose-response functions for the OTNAL intervention during spontaneously occurring real- life social gaze interactions and assess the corresponding changes in cerebrospinal fluid OT levels due to OTNAL compared to other conditions (Aim 1A, 1B). We will then study how neural activity patterns within and across two key brain nodes in social processing, the amygdala and the anterior cingulate cortex, are impacted by OTNAL (Aim 2). Finally, we will test causal contributions of these two regions for the OTNAL effects by blocking OT-binding receptor types focally in these areas (Aim 3). The results from this work will offer novel mechanistic insights into the combined pharmacological approach using OTNAL to more vigorously promote social engagements in the primate brain. Such results will help set the stage for translating the combinatorial benefit of using intranasal OTNAL for more effectively and reliably reducing core social symptoms in ASD.